Adds a platform independent detecion of microphone hardware mute

media/audio/audio_input_controller.cc

Index: media/audio/audio_input_controller.cc
diff --git a/media/audio/audio_input_controller.cc b/media/audio/audio_input_controller.cc
index c27e933c00fe407d0173c65c1e9cf80c91f07dc1..1b762999ef78a29710235c977ef5014746ecc408 100644
--- a/media/audio/audio_input_controller.cc
+++ b/media/audio/audio_input_controller.cc
@@ -10,13 +10,28 @@
 #include "base/threading/thread_restrictions.h"
 #include "base/time/time.h"
 #include "media/audio/audio_parameters.h"
-#include "media/base/limits.h"
 #include "media/base/scoped_histogram_timer.h"
 #include "media/base/user_input_monitor.h"
 
 using base::TimeDelta;
 
 namespace {
+
+// Logs if the user has enabled the microphone mute or not. This is normally
+// done by marking a checkbox in an audio-settings UI which is unique for each
+// platform. Elements in this enum should not be added, deleted or rearranged.
+enum MicrophoneMuteResult {
+  MICROPHONE_IS_MUTED = 0,
+  MICROPHONE_IS_NOT_MUTED = 1,
+  MICROPHONE_MUTE_MAX = MICROPHONE_IS_NOT_MUTED

[no longer working on chromium, 2014/09/22 10:16:35]

If you change MICROPHONE_MUTE_MAX = MICROPHONE_IS_NOT_MUTED + 1, then you can
just use MICROPHONE_MUTE_MAX in LogMicrophoneMuteResult

[henrika (OOO until Aug 14), 2014/09/22 11:24:13]

Found this style in other places in Chrome. Feels more intuitive to specify max
as the actual max and add 1 below. Let me know if you feel strongly about it.

[no longer working on chromium, 2014/09/23 08:17:58]

I think the most common style is
enum MicrophoneMuteResult {
  MICROPHONE_IS_MUTED = 0,
  MICROPHONE_IS_NOT_MUTED = 1,
  MICROPHONE_MUTE_MAX = 2
}

But this is just nit, feel free to keep what it is.

+};
+
+void LogMicrophoneMuteResult(MicrophoneMuteResult result) {
+  UMA_HISTOGRAM_ENUMERATION("Media.MicrophoneMuted",

[no longer working on chromium, 2014/09/22 10:16:35]

what is the follow-up after we get the muted or unmuted uma stats?

[henrika (OOO until Aug 14), 2014/09/22 11:24:13]

The idea is that we shall learn how many users actually do mute their microphone
this way. It adds one more piece to the big puzzle.

+                            result,
+                            MICROPHONE_MUTE_MAX + 1);
+}
+
 const int kMaxInputChannels = 3;
 
 // TODO(henrika): remove usage of timers and add support for proper
@@ -577,6 +592,19 @@ void AudioInputController::DoLogAudioLevels(float level_dbfs,
   if (microphone_volume_percent < kLowLevelMicrophoneLevelPercent)
     log_string += " <=> low microphone level!";
   handler_->OnLog(this, log_string);
+
+  // Try to detect if the user has enabled hardware mute by pressing the mute
+  // button in audio settings for the selected microphone. The idea here is to
+  // detect when all input samples are zeros but the actual volume slider is
+  // larger than zero. It should correspond to a hardware mute state.
+  if (level_dbfs == -std::numeric_limits<float>::infinity() &&
+      microphone_volume_percent > 0) {
+    LogMicrophoneMuteResult(MICROPHONE_IS_MUTED);
+    log_string = "AIC::OnData: microphone is muted!";
+    handler_->OnLog(this, log_string);
+  } else {
+    LogMicrophoneMuteResult(MICROPHONE_IS_NOT_MUTED);
+  }
 #endif
 }